1. Field of the Invention
The present invention relates to polyamide compositions useful in the manufacture of stain-resistant structures. More specifically, the polyamide compositions comprise modified homopolyamides and copolyamides which are prepared by salt-blending a base polyamide precursor salt with a cationic dye modifier and dyeing the resulting polymer with an acid dyestuff to a level of about 0.0048% or greater dyestuff concentration by weight. Fiber-forming and moldable polyamides including nylon 6,6, nylon 6, and nylon 6,6/6 copolymers are especially suitable base polymers for use in the present invention. The dyed polymers of the present invention are particularly useful in the manufacture of stain-resistant fibers and yarns for use in woven, knitted, or tufted textile materials as well as injection-molded products.
2. Prior Art
Polyamide textile materials which resist dyeing by acid dyestuffs are well-known in the art. Polyamide substrates may be rendered stain-resistant by treatment with a dye-resist agent, also referred to herein and in the prior art as a stain-resist agent, such as a sulfonated phenol- or sulfonated naphtol-formaldehyde condensation product. Such dye-resist agents have been applied to the fibers comprising the article as a coating from a spin finish; or the substrate in the form of a yarn or woven, knitted, or tufted fabric has been treated in a process wherein the stain-resist composition is applied via immersion, padding, spraying, or other application means in either a batch or continuous process. Such processes are useful for the production of woven, knitted, or tufted polyamide substrates which resist staining by various acid-dye colorants, such as those often present in foodstuffs. Because the aforementioned processes involve treatment of the fiber surface, these materials suffer from the disadvantage that the stain resistance tends to deteriorate with wear. Such processes also are not effective in the manufacture of cut-pile carpets in which the pile comprises hollow-filament or cellular polyamide yarns, because the surface treatment does not sufficiently protect the interior voids of the filament and tip-staining occurs as the solution is taken up by the filament voids via capillary action.
Japanese Patent Application Publication 1-223908, published Sep. 7, 1989, discloses stain-resistant polyamides based on nylon 6, nylon 6,6, nylon 4, nylon 7, nylon 11, nylon 6,10, etc., which contain a sulfonate-containing aromatic compound of the general formula ##STR1## where X is any of COOH, RCOOH, COOR', RCOOR', and RNH.sub.2 (R is a C.sub.1-5 alkylene group; R' is a C.sub.1-5 alkyl group); Z is an aromatic group; m and n are 1 or 2; M is hydrogen, an alkali metal or an ammonium group. Preferably the sulfonate group content is in the range of 0.1-5.0 mole % of the polyamide constituting units, with a terminal amino group content being not more than 10 eq/T.
It is known from Flamand U.S. Pat. No. 3,542,743, Crampsey, U.S. Pat. No. 3,640,942, Crovatt & Huffman, U.S. Pat. No. 3,440,226, and Ucci, U.S. Pat. No. 4,579,762 that polyamide materials may also be rendered resistant to staining by acid dyestuffs by copolymerizing the nylon with cationic dye modifiers such as aromatic sulfonates.